1. Field of the Invention
The present invention relates to a fusing device for use with an image forming device, which supplies toner to a latent image that is obtained by being exposed to light on a charged image carrier to form the latent image into an image and transfers a resultant toner image from the image carrier to a recording material, and for fixing the toner image on the recording material by applying a predetermined quantity of heat to the recording material, a heat generating device for making a heat generating member generate heat, an image forming device with the heat generating device and a temperature control method for controlling a temperature of the heat generating member.
2. Description of the Related Art
Conventionally, there has been provided a fusing device for performing a fusing treatment upon a recording material with a toner image being transferred thereto in an image forming device or the like. In the fusing device, a heat roller is heated by a heat source. Further, a recording material is conveyed while contacting the heat roller. Generation of heat from a lamp such as a halogen lamp built in the heat roller is usually utilized for the heat source. The heat source will be referred to as a fusing lamp hereinafter.
The fusing lamp is on-off controlled in order to maintain a surface temperature of the heat roller at a predetermined temperature. The fusing lamp becomes a factor of flicker caused by rush current generated when the fusing lamp is turned on and the heat roller starts to generate heat and when the fusing lamp is turned on during the control of the surface temperature of the heat roller.
In order to restrict the rush current of the fusing lamp, it is considered that a resistor is serially connected to the lamp when the fusing lamp starts to be lighted, so that the rush current is reduced by this resistor.
Nevertheless, the on-off control is frequently performed during the above-described temperature control. For this reason, in order to suppress repeatedly flowing the rush current, a resistor which can stand a large quantity of heat generation is required.
Especially a machine or the like such as a copying machine for large-scale drawings which is one of image forming devices requires a large quantity of power (800 W to 1,700 W). Thus, a resistor with a few hundreds watts of power is required to reduce a flicker and also, it becomes larger. The resistor itself generates a large quantity of heat and thus an atmosphere temperature within the machine becomes in an overheat state and the power is wastefully consumed. Thus, this atmosphere temperature and the consumption power may exceed their acceptable levels.
A prior art supposes that two lamps are serially placed in a heat roller and a number of lamps to be used is appropriately selected. (Japanese Patent Application Laid-Open (JP-A) No. 11-233235).
Japanese Patent Application Laid-Open (JP-A) No. 11-233235 describes only the case of warm-up and does not describe in detail when the two lamps should be selected in order to reduce a flicker and an on-off control of the two lamps. Thus, suppression of rush current at a time when a device starts to be operated may be expected to some extent (which is similar to a resistor inserting method) Nevertheless, Japanese Patent Application Laid-Open (JP-A) No. 11-233235 does not disclose a control method for suppressing a flicker generated during frequent on-off control in the operation of the device in a acceptable range.
The present invention is developed in light of the above-described facts and an object of the invention is to obtain a fusing device that, when a fusing treatment is performed by using a heat source with large power, is able to suppress a flicker generated during on-off control for maintaining a set temperature for the fusing treatment in an acceptable range.
Another object of the invention is to obtain a heat generating device and an image forming device that are able to suppress a flicker generated during on-off control for maintaining a set temperature of heat generating member in an acceptable range.
In addition to the aforementioned objects, yet another object of the invention is to obtain a temperature control method in which drawbacks of temperature control caused by a plurality of lamps being used at the same time (the heat generating member may be converged into two temperature levels at a time of the temperature control) can be solved and the heat generating member can be converged into a single set temperature.
A fusing device of the invention is for use with an image forming device, which supplies toner to a latent image that is obtained by being exposed to light on a charged image carrier to form the latent image into an image and transfers a resultant toner image from the image carrier to a recording material, and for fixing the toner image on the recording material by applying a predetermined quantity of heat to the recording material. The fusing device comprises: a heat roller which forms a portion of a conveyance path for the recording material and nips the recording material; a plurality of lamps which are accommodated within the heat roller and are connected in serial with each other and serve as heat sources; a switching component which classifies the plurality of lamps into at least a main lamp group and a sub-lamp group and is able to switch between application of electricity to the main lamp group and the sub-lamp group, application of electricity to only the main lamp group and application of electricity to neither the main lamp group nor the sub-lamp group; and a temperature control component which controls a temperature of the heat roller by controlling on or off switching of the plurality of lamps to control the power stage of the plurality of lamps with at least stages of off, low power and full power.
According to the fusing device of the invention, when the temperature of the heat roller can be controlled by one lamp group, a large quantity of power is required. For this reason, a rush current is generated when the one lamp group is switched on. Temperature control is performed by on-off control. Thus, a flicker is generated at a time of start of operation of the device as well as during operation of device.
Then, when switching on the lamp, the sub-lamp group which is connected in serial with the main lamp group is also switched on at the same time. For example, when the two lamp groups with the same power are serially connected with each other and turned on at the same time, a current flowing therethrough is half of current flowing when only one lamp group is lighted.
More specifically, when 500 W (100 V of rating) of lamp is lighted at 100 V, 5 A of current flows therethrough. Thus, a resistance R of this lamp is 20xcexa9 (W=I2R).
On the other hand, when 500 W (100 V of rating) of two lamps are serially connected with each other and lighted at 100 V, a total resistance R of these lamps is 20xcexa9+20xcexa9=40xcexa9 and thus 2.5 A of current flows therethrough (each of the lamp groups is lighted at 125 W).
In this way, a current can be suppressed. Thus, a rush current can be also reduced.
According to the fusing device of the invention, an added lamp for reducing a flicker is also utilized as a heat source. According to the temperature control component, three power stages, i.e., off, low power and full power are set so that temperature control is performed. Thanks to such temperature control, an overshoot can be reduced and the number of on-off switching can be also reduced. For example, when two lamps are connected in serial with each other, at a time of device being turned on, the power stage is in a low power state that two lamps are lighted at the same time. If desired, the power stage may be switched to an off state or a full power state that only one lamp is lighted.
A temperature control method of a first aspect of the invention is for controlling a temperature of a heat generating member by making the heat generating member generate heat in a plurality of power stages. the temperature control method of the first aspect comprises the steps of: setting a plurality of temperature areas for the heat generating member and setting a number of power stage to be increased/decreased for each of the temperature areas; detecting the temperature of the heat generating member; and increasing/decreasing, as necessary, the power stage by the number of power stage to be increased/decreased, which is set for the temperature area to which the temperature of the heat generating member belongs.
According to the temperature control method of the first aspect, there is provided, e.g., a temperature control method for controlling a temperature on a surface of a heat roller by selecting three power stages. A target temperature area for the heat roller is set in advance. Then, temperature areas are set at a higher temperature side of the target temperature area and at a lower temperature side of the target temperature area with the target temperature area at the middle of them. A current temperature on the surface of the heat roller is detected and it is determined to which temperature area the detected temperature belongs. In the determined temperature area, the power stage is increased/decreased by one stage. Thus, variation in the temperature on the surface of the heat roller is balanced on a basis of a quantity of heat transmitted to a recording material and it is controlled so that the detected temperature is converged into the target temperature area.
For example, lamps serving as heat sources for fusing are classified into two groups (hereinafter, each lamp group will be described as one lamp). Off, low power (two lamps are lighted) and full power (one lamp is lighted) are set as power stages (since the lamps are connected in serial with each other, a power generated when one lamp is lighted is larger than that generated when two lamps are lighted). In this case, according to a general temperature control, the power stage is uniquely set in proportion to the difference between the temperature on the surface of the heat roller detected by a temperature sensor and a target temperature and then temperature control is performed. Namely, two temperature areas are set at the higher temperature side of the target temperature and at the lower temperature side of the target temperature, respectively with the target temperature at the middle of them. The power stage is set in advance for each of the temperature areas.
Regardless of conditions (rate of change), the temperature on the surface of the heat roller enters these temperature areas and the power stage is switched to the power stage which is set in advance for these four temperature areas.
According to such temperature control, however, a rate of change in temperature of the heat roller relating to a quantity of heat taken by (transmitted to) the recording material is not considered.
Suppose that an initial temperature is in a second temperature area from the target temperature toward the lower temperature side and thus heating control is performed at full power (conditions).
If a quantity of heat taken is large, the temperature reaches a first temperature area from the target temperature toward the lower temperature side and the power stage is in a low power state. Since a quantity of heat taken is larger than that applied in a low power state of the power stage at this time, the temperature is not increased. Thus, an actual temperature is converged into the boundary between the first temperature area from the target temperature toward the lower temperature side and the second temperature area from the target temperature toward the lower temperature side (see solid line shown in FIG. 7).
On the other hand, if a quantity of heat taken is small under the same conditions as the aforementioned, the temperature exceeds the target temperature and reaches a second temperature area from the target temperature toward the higher temperature side. Thereafter, the power stage is in an off state and the temperature starts to be decreased. Then, in a first temperature area from the target temperature toward the higher temperature side, heating control is performed in a low power state. A quantity of heat applied in a low power state of the power stage exceeds a quantity of heat taken. For this reason, an actual temperature is converged into the boundary between the first temperature area from the target temperature toward the higher temperature side and the second temperature area from the target temperature toward the higher temperature side (see chain line shown in FIG. 7).
According to the temperature control method of the first aspect, for example, the temperature area is set at the higher temperature side of the target temperature and at the lower temperature side of the target temperature, respectively with the target temperature at the middle of them. In the respective temperature areas at the higher temperature side and at the lower temperature side, the power stage is set to be increased/decreased from the current power stage by one stage. Then, the heat roller is heated in a power stage which is increased/decreased by one stage on a basis of temperature area determined by a detected temperature on the surface of the heat roller.
Namely, the power stage is not determined as an absolute power with respect to each of the temperature areas but controlled so as to be increased/decreased by one stage from a current power stage. Accordingly, when the power stage is to be increased in the same temperature area, for example, the power stage is switched to a low power state if the current power stage is in an off state, and the power stage is switched to a full power state if the current power stage is in a low power state.
Because of such relative control, an actual temperature is converged into a vicinity of target temperature regardless of a quantity of heat taken by the recording material. Thus, stable temperature control can be performed.
A temperature control method of a second aspect of the invention, according to the temperature control method of the first aspect, wherein when the temperature area to which the temperature of the heat generating member belongs is a non-target temperature area adjacent to the target temperature area, the power stage is increased/decreased only in a case in which the temperature of the heat generating member has passed through a temperature area other than said adjacent non-target temperature area and the target temperature area and then enters said adjacent non-target temperature area for the first time.
According to the temperature control method of the second aspect, for example, the temperature areas are classified into two temperature areas at the higher temperature side of the target temperature area and at the lower temperature side of the target temperature area, respectively. When the determined temperature area is a temperature area near to the target temperature area, the power stage is maintained except for a case in which the surface temperature of the heat roller has passed through a temperature area other than said near temperature area and the target temperature area and then enters said near temperature area for the first time.
As described above, suppose that the temperature areas are classified into two temperature areas at the higher temperature side and at the lower temperature side, respectively. When the determined temperature area is a temperature area near to the target temperature area, the power stage is maintained except for a case in which the surface temperature of the heat roller has passed through a temperature area other than said near temperature area and the target temperature area and then enters said near temperature area for the first time. As a result, an amplitude of power can be reduced.
A heat generating device of the invention comprises: a heat generating member which includes a plurality of heat sources connected in serial with each other and generates heat by application of electricity to the heat source; and a heat generation control component which controls a state of application of electricity to the plurality of heat sources and makes the heat generating member generate heat in at least three power stages.
An image forming device of the invention comprises the heat generating device according of the invention. The image forming device is for supplying toner to a latent image that was obtained by being exposed to light on a charged image carrier to form toner image onto the image carrier and for transferring the toner image from the image carrier to the heated member, wherein the toner image is fixed onto a heated member by the heat generating member heating the heated member.